To meet the demand for wireless data traffic having increased since deployment of 4th-generation (4G) communication systems, efforts have been made to develop an improved 5th-generation (5G) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘beyond 4G network’ or a ‘post long term evolution (LTE) System’. The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), full dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems. In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, coordinated multi-points (CoMP), reception-end interference cancellation and the like. In the 5G system, hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM) modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
The Internet, which is a human centered connectivity network where humans generate and consume information, is now evolving to the Internet of things (IoT) where distributed entities, such as things, exchange and process information without human intervention. The Internet of everything (IoE), which is a combination of the IoT technology and the big data processing technology through connection with a cloud server, has emerged. As technology elements, such as “sensing technology”, “wired/wireless communication and network infrastructure”, “service interface technology”, and “Security technology” have been demanded for IoT implementation, a sensor network, a machine-to-machine (M2M) communication, machine type communication (MTC), and so forth have been recently researched. Such an IoT environment may provide intelligent Internet technology services that create a new value to human life by collecting and analyzing data generated among connected things. IoT may be applied to a variety of fields including smart home, smart building, smart city, smart car or connected cars, smart grid, health care, smart appliances and advanced medical services through convergence and combination between existing information technology (IT) and various industrial applications.
In line with this, various attempts have been made to apply 5G communication systems to IoT networks. For example, technologies, such as a sensor network, MTC, and M2M communication may be implemented by beamforming, MIMO, and array antennas. Application of a cloud RAN as the above-described big data processing technology may also be considered to be as an example of convergence between the 5G technology and the IoT technology.
In the recent years, several broadband wireless technologies have been developed to meet the growing number of broadband subscribers and to provide more and better applications and services. The second generation wireless communication system has been developed to provide voice services while ensuring the mobility of users. Third generation wireless communication system supports not only the voice service but also data service. In recent years, the fourth wireless communication system has been developed to provide high-speed data service. However, currently, the fourth generation wireless communication system suffers from lack of resources to meet the growing demand for high speed data services.
A method of providing a generally high data transmission rate includes a method of providing communication using a wider frequency band and a method of increasing frequency usage efficiency. However, it is very difficult to provide a higher average data rate through the latter method. This is because communication technologies of a current generation provide frequency usage efficiency close to a theoretical limit and thus, it is very difficult to increase the frequency usage efficiency up to that or more through a technical improvement. Accordingly, it can be said that a feasible method for increasing the data transmission rate is a method of providing data services through the wider frequency band. At this time, the thing to consider is an available frequency band. In view of the current frequency distribution policy, a band in which a broadband communication of 1 GHz or more is possible is limited and a practically selectable frequency band is only the millimeter wave band of 30 GHz or more. Such a signal of the high frequency band causes severe signal attenuation according to a distance differently from a signal of a frequency band of 2 GHz used by the cellular systems of the related art. Due to such signal attenuation, service providing coverage of a base station using the same power as the cellular systems of the related art will be considerably reduced. In order to solve this problem, a beam forming technique is widely used which concentrates transmission/reception power into a narrow space to increase transmission/reception efficiency of an antenna.
Due to high path loss, heavy shadowing and rain attenuation reliable transmission at higher frequencies is one of the key issues that need to be overcome in order to make the millimeter wave systems a practical reality. The lower frequencies in cellular band having robust link characteristics can be utilized together with higher frequencies in mmWave band to overcome the reliability issues.
FIG. 1 illustrates a deployment of a wireless communication system using higher frequencies according to the related art.
Referring to FIG. 1, high frequency small cells are deployed in coverage of low frequency (LF) macro cell. Mobile station (MS) first connects with LF base station (BS)/eNB (master BS/eNB). LF BS/ENB adds high frequency (HF) BS (secondary BS) to meet quality of service (QoS) requirements high data rate (HDR). A user equipment (UE) communicates with both master BS/eNB and Secondary BS/eNB.
A typical procedure of adding a secondary BS in prior art is shown in FIG. 2 according to the related art.
FIG. 2 is a signal flow diagram illustrating a typical procedure of adding a secondary base station according to the related art.
Referring to FIG. 2, a master eNB (MeNB) decides to add a secondary eNB (SeNB) based on measurement result from the UE and sends addition request to the SeNB. The SeNB performs admission control and sends acknowledgement with the SeNB radio resource configuration. The MeNB sends the RRCConnectionReconfiguration message to the UE including the new radio resource configuration of the SeNB according to the SCG-Config. The UE applies the new configuration and replies with RRCConnectionReconfigurationComplete message. The MeNB informs the SeNB that the UE has completed the reconfiguration procedure successfully. The UE performs Uplink synchronisation towards the SeNB using the random access procedure. After the random access procedure, the UE may start transmitting and receiving the data from the SeNB.
In a beamformed system, the control plane operation is performed in a beam formed manner. In such a system, sending of the random access preamble (RACH) and the random access response (RAR) is also performed in a beam formed manner. However since at the time of random access procedure the best beams on which to operate are not known, the procedure typically involves sending the same information on multiple beams and attempted to be received by the receiver using all its receive beams. After this procedure, the best beams for transmission and reception are known at both the receiver and the transmitter. However this procedure is time consuming since it involves sending and receiving same information over multiple beams. Since future systems are required to achieve ultra-low latency and since random access is a typical process for establishment of data transfer, it is of utmost importance to optimize it to the maximum.
Therefore, a need exists for an enhanced random access procedure considering the beam forming.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.